Tracking Herbicide Resistance in Weed Evolution  

By Emily McKay Johnson, Associate Editor

Marie Jasieniuk, professor and weed scientist at UC Davis College of Agricultural and Environmental Sciences, discussed her groundbreaking research, “I work on the population genetics and evolution of agricultural weeds and invasive plants,” she said. “We use molecular tools to look at the origins and spread of weeds. We also use molecular tools and genetic studies to understand the evolution of herbicide resistance in weeds,” Jasieniuk added, “to be able to propose management approaches that reduce the likelihood of further evolution and spread of resistant weeds.”

UC Davis Annual Weed Day 2016

Jasieniuk and her team identify the origins of invasive plants, and determine how they were introduced. “We study how they were introduced, how they have spread and whether they have been introduced multiple times. Again, if we understand how they’re spreading, we can do something to try to stop the spread,” she said.

Italian rye grass, a weed Jasieniuk is currently studying, is problematic because it is resistant to Roundup, a popularly used weed and grass killer by growers. “UC ANR Cooperative Extension specialist, now emeritus, Tom Lanini, and I sampled over 100 locations of Italian rye grass and tested them for resistance to Roundup ten years ago,” she said about the project, funded by USDA. “Last year, we re-sampled all of those sites, and we’re re-testing to see if there’s been an increase or a decrease or no change in resistance to glyphosate, to Roundup,” she said.

Roundup isn’t the only weed and grass killer available on the market. “We’re looking at resistance to three other herbicides,” she said. Working with growers to determine the most efficacious weed treatments that also reduce the likelihood of wood resistance to herbicides,” Jasieniuk explained, “We interview growers about their herbicide use, non-chemical approaches, and integrated management techniques to identify management practices that correlate highly with low or no resistance,” she explained.

Resistance management is found to be more effective with a rotation of various herbicides. “What you want to do is rotate different types of herbicides with different modes of action,” Jasieniuk said. “Perhaps do tank mixes and incorporate non-chemical approaches as well,” she added.

Eliminating weeds can be as simple as disking and digging them out with a shovel when there are only a few. “I think, in many cases, this would have done a lot to prevent new weeds from coming in and certainly resistant weeds from spreading,” she noted.